This invention relates in general to means for prevention of contamination of structures during manufacturing and, more specifically, to covers for openings in complex structures such as missiles and aircraft to prevent entry of contaminants during further machining or other manufacturing operations.
In the manufacture of aircraft, missiles and other complex structures, it is often necessary to partially assemble the structure, perform machining steps, then continue with assembly and installation of parts. Access to compartments, such as fuel tanks, is provided by openings which eventually are covered by plate-like covers, secured by a ring of bolts around the edge of the opening. These openings are not covered during assembly and machining, since access is needed from time to time and periodically removing and reinstalling the ring of bolts is time consuming and can lead to bolt hole thread damage.
If these compartment openings are left open during the assembly and machining operations, contaminants such as water, oil, metal chips or filings or the like will enter the compartments. These contaminants must be very thoroughly cleaned from the compartments prior to use of the finished structure, especially where the compartment contains electronics components or fuel. Perfect cleaning of these compartments, if highly contaminated, is very difficult in a fully assembled, very complex, structure.
In the past, such openings were covered by taping brown kraft paper over them. Cutting paper covers to shape and the manual taping operation are labor intensive and thus costly. Tape will sometimes not adhere to slightly oily surfaces and the paper will sometimes tear, permitting access of contaminants. Removing and reinstalling such paper covers each time access to a compartment was needed is time consuming and inefficient.
Solid rubber or plastic plugs have been used to close openings, especially in electrical connectors or the like. These are not useful in non-standard sized or shaped openings and tend to be loose and prone to falling out if the structure is inverted.
Attempts have been made to force soft foam balls, such as the popular "Nerf" balls into such openings. While such plugs are adaptable to a variety of opening sizes and shapes, they have been found to flake or abrade off foam particles when inserted and removed from sharp-edged openings, with the resulting particles adding to the contamination problem. Also, plugs of this type do not protect the ring of bolt holes often present around an access opening from contamination.
Thus, there is a continuing need for improved temporary contamination preventing plugs for access openings in complex aerospace structures during manufacture and assembly operations.